1. Field of the Invention
The present invention relates to an optical repeating device with a monitoring function to be inserted in an optical transmission line such as optical fibers, and so forth for detecting lightwave signals being transmitted through the optical transmission line.
2. Description of the Related Art
Conventional technologies in this field have been described in, for example, the following documents.
Document 1: Japanese Patent Publication No. H3-60090;
Title of the Invention; Optical Connector
Publication Date; Sep. 12, 1991
Document 2: Japanese Utility Model Registration No. 2586555;
Title of the Invention; Optical Demultiplexer-Multiplexer
Registration Date; Oct. 2, 1998
A technology related to an optical connector for connecting two lengths of optical fibers with each other is described in Document 1. The optical connector comprises a pair of ferrules, each attached to the tip of the respective lengths of the optical fibers to be connected with each other and having a part to be grasped, a guide member for causing the pair of the ferrules to be inserted, therethrough and secured thereby by moving the same in the direction of a coupling axis, and for aligning the core axes of the both lengths of the optical fibers with each other, and a housing for securely holding the pair of the ferrules, formed independently from the guide member. The housing for securely holding the pair of the ferrules is formed of a metal sheet of uniform thickness, having a bottom portion which is a flat section, and a grasping part having elasticity, vertically upstanding from the bottom portion at opposite ends thereof, respectively, and the respective grasping parts are provided with a groove into which the pair of the ferrules inserted through the guide member are fitted, respectively. When the pair of the ferrules are fitted into the respective grooves, the respective grasping parts and the bottom portion undergo deformation in an arched shape, whereupon an elastic force developed presses the respective parts to be grasped such that the pair of the ferrules are butted against each other in the direction of the respective core axes by the agency of the respective grasping parts.
With the optical connector as described in Document 1, since it is constructed such that coated optical fibers are connected with each other in a condition wherein the same are butted against each other in the direction of the respective core axes by simply fitting the pair of the ferrules inserted through a sleeve into the housing for securely holding the pair of the ferrules, it is possible to downsize the optical connector, and further to facilitate assembling and disassembling of the optical connector. Further, since the sleeve and the housing for securely holding the pair of the ferrules are formed independently from each other, it is possible to align satisfactorily the core axes of the coated optical fibers with each other by the sleeve without being affected by other external forces.
Now a technology related to an optical demultiplexer-multiplexer with a filter block mounted in a case thereof is described in Document 2. With the optical demultiplexer-multiplexer, the filter block is mounted on a single island-like portion of a mounting surface of the case, formed by cutting a groove around the periphery thereof, and having a surface area smaller than that of the bottom of the filter block.
With the optical demultiplexer-multiplexer according to Document 2, since the single island-like portion for mounting the filter block thereon is formed on the mounting surface of the case by cutting the groove around the periphery thereof, the island-like portion constituted as a fixture mount for the filter block is simple in structure, and also, can be formed with ease. Further, as the filter block is mounted on the island-like portion having the surface area smaller than that of the bottom of the filter block, high stability in performance of the optical demultiplexer-multiplexer against variation in temperature is obtained.
In the past, there have been used an optical repeating device for detecting whether or not lightwave signals are transmitted through an optical transmission line, comprising in combination, for example, an optical branch, optical fibers, photo diode (referred to hereinafter as PD), light emitting diode (referred to hereinafter as LED), and so forth. In this connection, the optical branch is to branch off a portion of a lightwave signal being transmitted through the optical transmission line by use of a half mirror, and so forth, and is made up using technologies such as the technology described in Document 2. Then, a lightwave signal, branched off by the optical branch, is taken into the optical fibers, and the lightwave signal, taken into the optical fibers, is converted into an electric signal by the PD. The electric signal as converted is displayed as a visible signal by the LED. As a result, it has been possible to detect whether or not the lightwave signal is transmitted through the optical transmission line by visually watching such a display.
However, with the conventional optical repeating device, the following problems have been encountered.
That is, since the conventional optical repeating device comprises in combination a plurality of optical devices such as the optical branches, PDs, and so forth, there is a tendency of the number of devices increasing while requiring the optical connector, and so forth, made up using the technology described in Document 1, and the like for connecting these devices with each other Consequently, it has been difficult to achieve downsizing of the optical repeating device.
It is therefore a first object of the invention to simplify and downsize the construction of a housing by providing optical branching means for branching off, and reflecting a portion of a lightwave signal propagating through first optical propagation means and second optical propagation means in a given direction, and by disposing photodetection means such as PDs on the optical axis of the lightwave signal reflected, and also to provide an optical repeating device with a monitoring function, wherein the first optical propagation means, second optical propagation means, photodetection means, and so forth are assembled into the housing, and integrated therewith, so that needs for connecting devices such as optical connectors are eliminated, thereby enabling a whole structure to be simplified and downsized.
A second object of the invention is to provide an optical repeating device with a monitoring function, wherein the first optical propagation means and the second optical propagation means are made up of a relaying optical fiber, and a ferrule formed of a transmissive member for covering the periphery of the relaying optical fiber for protection, respectively, so that the lightwave signal reflected by the optical branching means is allowed to pass through the ferrule formed of the transmissive member so as to be guided with ease to the photodetection means.
A third object of the invention is to provide an optical repeating device with a monitoring function, wherein the optical branching means are made up by forming a metallic film or a multi-layered dielectric coating on respective branching faces of the first optical propagation means and the second optical propagation means by vapor deposition, so that assembling and adjustment work to be performed when joining the first optical propagation means and the second optical propagation means together can be simplified.
A fourth object of the invention is to provide an optical repeating device with a monitoring function, wherein the optical branching means for reflecting a portion of the lightwave signal propagated from the first optical propagation means in a first direction relative to the optical axis of the lightwave signal, and for reflecting a portion of the lightwave signal propagated from the second optical propagation means in a second direction, opposite from the first direction, are provided, so that lightwave signals transmitted through an optical transmission line can be detected by direction by adopting a constitution such that the lightwave signal can be taken out by direction through the optical branching means.
A fifth object of the invention is to provide an optical repeating device with a monitoring function, wherein display means for displaying in a visible condition whether or not a lightwave signal is present are provided, thereby enabling whether or not the lightwave signal is present to be checked with ease.
A sixth object of the invention is to provide an optical repeating device with a monitoring function, wherein the photodetection means can be disposed with ease by forming first and second branching faces to be inclined at angle of, for example, 45 degrees relative to the optical axis of the lightwave signal, and by reflecting a portion of the lightwave signal, branched off, in the orthogonal direction, so that the construction of the housing can be simplified and downsized.
To this end, in accordance with a first aspect of the invention, there is provided an optical repeating device with a monitoring functional comprising first optical propagation means having a first end face for connection with a first optical fiber among the first optical fiber and a second optical fiber, constituting an optical transmission line, and a first branching face formed at a predetermined angle relative to the optical axis of a lightwave signal for branching the lightwave signal transmitted from the first optical fiber, second optical propagation means having a second end face for connection with the second optical fiber of the optical transmission line, and a second branching face formed at the predetermined angle against the optical axis of a lightwave signal for branching the lightwave signal transmitted from the second optical fiber, optical branching means provided between the first branching face of the first optical propagation means, and the second branching face of the second optical propagation means, in intimate contact with each other, for allowing a large portion of the lightwave signal propagated between the first optical propagation means and the second optical propagation means to pass therethrough while reflecting a portion of the lightwave signal in a given direction relative to the optical axis of the lightwave signal, photodetection means for detecting a lightwave signal reflected by the optical branching means, and outputting an electric signal at a level corresponding to intensity of the lightwave signal, and a housing for housing therein the first optical propagation means, the second optical propagation means, the optical branching means, and the photodetection means at predetermined positions to be securely held thereto.
With these features, the optical repeating device with the monitoring function according to the invention may have a constitution such that the first optical propagation means are made up of a first relaying optical fiber for relaying a lightwave signal between the first end face for connection with the first optical fiber and the first branching face, and a first ferrule formed of a transmissive tubular member for securely holding the first relaying optical fiber to a predetermined position therein for protection (that is, covering the periphery of the first relaying optical fiber for protection) while the second optical propagation means are made up of a second relaying optical fiber for relaying a lightwave signal between the second end face for connection with the second optical fiber and the second branching face, and a second ferrule formed of a transmissive tubular member for securely holding the second relaying optical fiber to a predetermined position therein for protection (that is, covering the periphery of the second relaying optical fiber for protection).
Further, in addition to any of these features described above, the optical branching means may be made up by forming a metallic film or a multi-layered dielectric coating on the respective branching faces of the first optical propagation means and the second optical propagation means by vapor deposition.
With the optical repeating device with the monitoring function according to the invention, constituted as described in the foregoing, a large portion of a lightwave signal inputted from the first optical fiber of the optical transmission line to the first end face of the first optical propagation means comprising the relaying optical fiber protected by, for example, the ferrule is propagated from the first branching face of the first optical propagation means to the second branching face of the second optical propagation means via the optical branching means, and is then outputted from the second end face of the second optical propagation means to the second optical fiber. At this point in time, a portion of the lightwave signal inputted to the first end face of the first optical propagation means is branched off by the optical branching means, for example, the metallic film formed on the first branching face by vapor deposition, and is reflected in a given direction relative to the optical axis of the lightwave signal. The lightwave signal reflected by the optical branching means is detected by the photodetection means, and an electric signal at a level corresponding to intensity of the lightwave signal is outputted.
Preferably, the optical branching means are set to allow a large portion of the lightwave signal propagated to the first optical propagation means and the second optical propagation means, respectively, to pass therethrough while reflecting a portion of the lightwave signal propagated from the first optical propagation means in a first direction, and reflecting a portion of the lightwave signal propagated from the second optical propagation means in a second direction, opposite from the first direction.
With the invention constituted as above, a large portion of the lightwave signal inputted to the first end face of the first optical propagation means is propagated from the first branching face of the first optical propagation means to the second branching face of the second optical propagation means via the optical branching means, and is then outputted from the second end face of the second optical propagation means to the second optical fiber. At this point in time, a portion of the lightwave signal inputted to the first end face is reflected in the first direction by the optical branching means. Meanwhile, a large portion of the lightwave signal inputted from the second optical fiber of the optical transmission line to the second end face of the second optical propagation means is propagated from the second branching face of the second optical propagation means to the first branching face of the first optical propagation means via the optical branching means, and is then outputted from the first end face of the first optical propagation means to the first optical fiber. At this point in time, a portion of the lightwave signal inputted to the second end face is reflected in the second direction by the optical branching means. The lightwave signals reflected in the first and second directions, respectively, are detected by the photodetection means, and electric signals at levels corresponding to intensity of the respective lightwave signals are outputted.
Further, in addition to any of those features described in the foregoing, the optical repeating device with the monitoring function according to the invention may be provided with display means securely held to the housing to display in a visible condition whether or not the lightwave signal is transmitted through the optical transmission line on the basis of the electric signal outputted from the photodetection means. As a result, the electric signal outputted from the photodetection means is provided with the display means, so that whether or not the lightwave signal is present in the optical transmission line can be displayed in a visible condition.
Still further, with the optical repeating device with the monitoring function according to the invention, having any of the features described in the foregoing, the first branching face of the first optical propagation means, and the second branching face of the second optical propagation means are preferably formed so as to form an angle of 45 degrees relative to the optical axis of the lightwave signal. As a result, the lightwave signal is reflected in the direction orthogonal to the optical axis to be branched.